Abstract: A multi-role, long-endurance, vertical takeoff and landing tiltrotor composite fixed-wing UAV is designed. Maximum takeoff weight is 30 kg, and extended duration of flight is over 24 hours. Conceptual design, aerodynamic analysis and structure design of the UAV are completed. Static loading test of middle wing section is carried out, which is compared with numerical analysis data. Based on finite element analysis, the strength, stiffness and stability of the airframe are checked. Hashin failure criterion is used to determine the damage of carbon fiber panel and balsa wood core of composite sandwich structure, carbon fiber skin is also checked. Wing skin laminate design is optimized, and structure performance is assessed. It is showed that climbing by 2.5g load with pay load below the fuselage is the severest load case. High stress state is found in the center aera of the middle wing. Buckling tends to occur firstly at the upper skin of the middle wing. Initial structure damage mode is compression damage of balsa core. Performance requirements with excessive load margin is satisfied by initial composite laminate layup. Wing skin laminate layup is optimized by sub-region semi equi-strength design. Weight of the wing is reduced by 1.51 kg, about 17% decrease. Wing load margin is reduced to 0.13 which shows outstanding improvement of structure loading efficiency. The endurance of the UAV is estimatedby energy consumption relationship.

Key words: composite, VTOL, tiltrotor, fixed wing, UAV